diff options
Diffstat (limited to 'gas/doc/c-i386.texi')
| -rw-r--r-- | gas/doc/c-i386.texi | 19 |
1 files changed, 15 insertions, 4 deletions
diff --git a/gas/doc/c-i386.texi b/gas/doc/c-i386.texi index e27893b..8a9c85a 100644 --- a/gas/doc/c-i386.texi +++ b/gas/doc/c-i386.texi @@ -443,14 +443,25 @@ instructions is reversed from the Intel syntax. @cindex i386 16-bit code @cindex 16-bit code, i386 @cindex real-mode code, i386 +@cindex @code{code16gcc} directive, i386 @cindex @code{code16} directive, i386 @cindex @code{code32} directive, i386 While @code{@value{AS}} normally writes only ``pure'' 32-bit i386 code, it also supports writing code to run in real mode or in 16-bit protected -mode code segments. To do this, put a @samp{.code16} directive before -the assembly language instructions to be run in 16-bit mode. You can -switch @code{@value{AS}} back to writing normal 32-bit code with the -@samp{.code32} directive. +mode code segments. To do this, put a @samp{.code16} or +@samp{.code16gcc} directive before the assembly language instructions to +be run in 16-bit mode. You can switch @code{@value{AS}} back to writing +normal 32-bit code with the @samp{.code32} directive. + +@samp{.code16gcc} provides experimental support for generating 16-bit +code from gcc, and differs from @samp{.code16} in that @samp{call}, +@samp{ret}, @samp{enter}, @samp{leave}, @samp{push}, @samp{pop}, +@samp{pusha}, @samp{popa}, @samp{pushf}, and @samp{popf} instructions +default to 32-bit size. This is so that the stack pointer is +manipulated in the same way over function calls, allowing access to +function parameters at the same stack offsets as in 32-bit mode. +@samp{.code16gcc} also automatically adds address size prefixes where +necessary to use the 32-bit addressing modes that gcc generates. The code which @code{@value{AS}} generates in 16-bit mode will not necessarily run on a 16-bit pre-80386 processor. To write code that |